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- Author or Editor: S. Sharma x
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Abstract
Laser scintillation observations were carried out over a flat surface in different atmospheric conditions on 33 separate days during March 1990–April 1991 and were analyzed and studied. The principal results of the analysis reveal (i) marked seasonal variations in optical turbulence (through the measurement of refractive-index structure function Cn 2) and scintillation intensity (measured in terms of percent modulation Pm ) with maximum Cn 2 or Pm during winter (December–February) and minimum during premonsoon (March–May) seasons; (ii) close correspondence among the variations in Cn 2, Pm , and atmospheric temperature; (iii) lower values of Cn 2 during cloudy sky as compared to clear sky conditions; and (iv) agreement between the observations and theory in respect of the pathlength dependence of Cn 2 and Pm . The results are discussed with reference to the possible meteorological origin of turbulence, and the importance of the study for making measurements of optical turbulence remotely over inaccessible regions is highlighted.
Abstract
Laser scintillation observations were carried out over a flat surface in different atmospheric conditions on 33 separate days during March 1990–April 1991 and were analyzed and studied. The principal results of the analysis reveal (i) marked seasonal variations in optical turbulence (through the measurement of refractive-index structure function Cn 2) and scintillation intensity (measured in terms of percent modulation Pm ) with maximum Cn 2 or Pm during winter (December–February) and minimum during premonsoon (March–May) seasons; (ii) close correspondence among the variations in Cn 2, Pm , and atmospheric temperature; (iii) lower values of Cn 2 during cloudy sky as compared to clear sky conditions; and (iv) agreement between the observations and theory in respect of the pathlength dependence of Cn 2 and Pm . The results are discussed with reference to the possible meteorological origin of turbulence, and the importance of the study for making measurements of optical turbulence remotely over inaccessible regions is highlighted.
Abstract
Coordinated experiments to study the nocturnal lower atmosphere were conducted on selected nights during April–August 1991 using an argon ion lidar and a Doppler sodar at the Indian Institute of Tropical Meteorology, Pune (18°32′N, 73°51′E, 559 m MSL), India. The lidar and the sodar have been operated simultaneously so as to detect the nocturnal atmospheric structure in the common air volume sampled by both the techniques. By analyzing the thermal and aerosol structures in the vertical profiles of the sodar and the lidar signal intensity, the nocturnal mixed-layer height or ground-based inversion height and the stably stratified or multiple elevated layers aloft have been determined. The top of the nocturnal ground-based inversion observed in the sodar records is taken as the height above the ground where the negative vertical gradient in aerosol concentration first reaches a maximum in the lidar records. The results of the study indicate an agreement between the lidar-derived mixing depth and the sodar-derived heights of the ground-based inversion and the low-level wind maximum.
Abstract
Coordinated experiments to study the nocturnal lower atmosphere were conducted on selected nights during April–August 1991 using an argon ion lidar and a Doppler sodar at the Indian Institute of Tropical Meteorology, Pune (18°32′N, 73°51′E, 559 m MSL), India. The lidar and the sodar have been operated simultaneously so as to detect the nocturnal atmospheric structure in the common air volume sampled by both the techniques. By analyzing the thermal and aerosol structures in the vertical profiles of the sodar and the lidar signal intensity, the nocturnal mixed-layer height or ground-based inversion height and the stably stratified or multiple elevated layers aloft have been determined. The top of the nocturnal ground-based inversion observed in the sodar records is taken as the height above the ground where the negative vertical gradient in aerosol concentration first reaches a maximum in the lidar records. The results of the study indicate an agreement between the lidar-derived mixing depth and the sodar-derived heights of the ground-based inversion and the low-level wind maximum.
Abstract
The interaction of global climate change and urban heat islands (UHI) is expected to have far-reaching impacts on the sustainability of the world’s rapidly growing urban population centers. Given that a wide range of spatiotemporal scales contributed by meteorological forcing and complex surface heterogeneity complicates UHI, a multimodel nested approach is used in this paper to study climate-change impacts on the Chicago, Illinois, UHI, covering a range of relevant scales. One-way dynamical downscaling is used with a model chain consisting of global climate (Community Atmosphere Model), regional climate (Weather Research and Forecasting Model), and microscale (“ENVI-met”) models. Nested mesoscale and microscale models are evaluated against the present-day observations (including a dedicated urban miniature field study), and the results favorably demonstrate the fidelity of the downscaling techniques that were used. A simple building-energy model is developed and used in conjunction with microscale-model output to calculate future energy demands for a building, and a substantial increase (as much as 26% during daytime) is noted for future (~2080) climate. Although winds and lake-breeze circulation for future climate are favorable for reducing energy usage by 7%, the benefits are outweighed by such factors as exacerbated UHI and air temperature. An adverse change in human-comfort indicators is also noted in the future climate, with 92% of the population experiencing thermal discomfort. The model chain that was used has general applicability for evaluating climate-change impacts on city centers and, hence, for urban-sustainability studies.
Abstract
The interaction of global climate change and urban heat islands (UHI) is expected to have far-reaching impacts on the sustainability of the world’s rapidly growing urban population centers. Given that a wide range of spatiotemporal scales contributed by meteorological forcing and complex surface heterogeneity complicates UHI, a multimodel nested approach is used in this paper to study climate-change impacts on the Chicago, Illinois, UHI, covering a range of relevant scales. One-way dynamical downscaling is used with a model chain consisting of global climate (Community Atmosphere Model), regional climate (Weather Research and Forecasting Model), and microscale (“ENVI-met”) models. Nested mesoscale and microscale models are evaluated against the present-day observations (including a dedicated urban miniature field study), and the results favorably demonstrate the fidelity of the downscaling techniques that were used. A simple building-energy model is developed and used in conjunction with microscale-model output to calculate future energy demands for a building, and a substantial increase (as much as 26% during daytime) is noted for future (~2080) climate. Although winds and lake-breeze circulation for future climate are favorable for reducing energy usage by 7%, the benefits are outweighed by such factors as exacerbated UHI and air temperature. An adverse change in human-comfort indicators is also noted in the future climate, with 92% of the population experiencing thermal discomfort. The model chain that was used has general applicability for evaluating climate-change impacts on city centers and, hence, for urban-sustainability studies.
